Burner and method for the chemical reaction of two gas streams

ABSTRACT

The invention relates to a burner with a burner head ( 1 ) and a gas feed pipe ( 2 ) that is located in the burner head ( 1 ) and that is surrounded by an ring channel ( 3 ) for feed of another gas. In the gas feed pipe ( 2 ) and in the ring channel ( 3 ), there are means ( 10, 11 ) for producing a swirl of the gas flowing through the gas feed pipe ( 2 ) and that flowing through the ring channel ( 3 ).

The invention relates to a burner with a burner head and a gas feed pipethat is located in the burner head and that is surrounded by a ringchannel for feed of another gas, in the gas feed pipe and in the ringchannel there being means for producing a swirl of a gas flowing throughthe gas feed pipe or a gas flowing through the ring channel.Furthermore, the invention relates to a process for producing a reactionproduct by chemical reaction of gases that are supplied to a reactionspace by means of a burner as two separate gas streams and arechemically reacted in the reaction space.

When a combustible gas is burned with an oxygen-containing gas in anoutside-mixing burner, i.e. in burners in which the combustible gas andthe oxygen-containing gas are not premixed, but are routed separatelyinto the mixing zone and are ignited there, it is important to achieveintensive intermixing of the oxygen-containing gas and combustible gasin order to accelerate the chemical combustion reaction between thesegases.

In U.S. Pat. No. 5,492,649, it is therefore proposed that a swirl beimpressed on the oxygen-containing gas before entering the mixing zone.In this process, a recirculation zone forms as the oxygen-containing gasis highly swirled in front of the exit opening of the oxygen-containinggas. In other words: with strong rotary momentum of theoxygen-containing gas, the latter has a flow profile in which in thevicinity of the flow axis, the flow direction is reversed and backflowforms. Intensive turbulence that promotes the chemical reaction betweenthe combustible gas and the oxygen-containing gas results from the steepvelocity gradient in the transition area between the forward flow andthe backflow.

Within the framework of extensive studies preceding this invention, ithas been found, however, that the backflow in the axial area also takesin hot reaction gases that then travel to the exit opening of the feedpipe for the oxygen-containing gas. The hot reaction gases attack thegas feed pipe so that the feed pipe is damaged.

The object of this invention is therefore to develop a burner and aprocess for chemical reaction of gases, damage to the burner beingavoided as much as possible and the chemical reaction taking place asefficiently and in as defined a manner as possible.

This object is achieved by a burner of the initially mentioned type, inwhich the wall of the gas feed pipe runs to an acute angle on its exitend and the means for producing a swirl in the gas feed pipe or the ringchannel is set back upstream against the exit end by 0.1 to 10 times,preferably by 0.5 to 5 times, and especially preferably by 0.5 to 2times the outside diameter of the means for producing a swirl.

Damage to the burner tip can essentially be attributed to the backflowof hot gases. It has been found that one of the reasons for suchbackflows lies in the execution of the exit end of the gas feed pipe.According to the invention, the wall of the gas feed pipe runs out to anacute angle on the exit end, i.e., its wall thickness graduallydiminishes to a value of almost zero.

This embodiment greatly reduces the danger of separation of the gasstreams emerging from the gas feed pipe and the ring channel in the areaof the exit end of the gas feed pipe. The flow filaments do not detachat the exit end of the gas feed pipe and do not cause eddies that canlead to unwanted heat delivery to the burner tip.

For highly varied velocities of the gases supplied via the gas feed pipeand via the ring channel, however, eddies can still separate. Thisadverse effect also occurs when the speed of one of the participatinggases is changed, as can occur, for example, when the load changes.

It has now been shown that the flow in the use of swirl bodies accordingto the invention, i.e., the means for producing a swirl, in the gas feedpipe and the ring channel breaks away in part on the exit end of the gasfeed pipe and eddies form. Studies have shown that the component ofrotary motion that has been impressed on the gas streams as swirling isproduced directly following the swirl bodies and has in alternationareas with higher velocity and areas with lower velocity. That is,tangentially to the direction of primary flow of the gas, gas velocitypeaks and valleys periodically occur. These velocity changes on the exitend of the gas feed pipe are causally responsible for the unwanted flowseparation.

Therefore, according to the invention, the means for producing a swirlare set back relative to the exit end of the gas feed pipe, i e., arelocated upstream from it. The distance to the exit opening is between0.1 and 10 times, preferably between 0.5 and 5 times, and especiallypreferably between 0.5 and 2 times the inside diameter of the gas feedpipe. A distance from 1.5 to 2.5 of the outside diameter of the swirlgeneration means has proven quite especially effective. In this way, theabove-described periodic velocity changes are equalized and on the exitend a flow profile forms with an essentially constant peripheral speed.The swirl generation means in the ring channel are likewise set backrelative to the exit opening of the ring channel. Here, a distance from0.5 to 1 times the outside diameter of the swirl generation means thatis located in the ring channel has proven favorable.

A process of the initially mentioned type for chemical reaction of gasesis characterized according to the invention in that before entering thereaction space, a swirl flow is impressed on the gas streams in eachcase, i.e., the gas streams also have a component of rotary motionaround the direction of their main flow upon entering the reactionspace, in addition to the essentially axial component of motion.

The additional swirling of the gas supplied via the ring channelaccording to the invention leads to intensive radial mass exchangebetween the two gas streams and thus to rapid mixing. The inner jet isfocussed by the outer jet that is widened conversely by the inner jet.This strong interaction between the two jets causes intensive and rapidmixing.

In the overall jet in the region of the burner, in this case backflowzones do not form, so that hot reaction gas is largely kept away fromthe gas feed pipe. Only the relatively cold, not yet reacted gases comeinto direct contact with the gas feed pipe. Damage to the gas feed pipeby convection is prevented.

The invention allows exactly definable mixing of the participating gasstreams. In the reaction space in which the chemical reaction is to takeplace, the temperature, flow and gas composition conditions can bematched to the desired chemical reactions. The widening of the flamethat forms in the reaction of the two gas streams can be adjusted viathe strength of the two swirl flows within wide limits. The shape of theflame can be made as desired by the swirl flow according to theinvention. Thus, optimum matching to the size of the reaction space ispossible. Furthermore, the dwell time in the reaction space can beoptimized by suitable choice of flow guidance.

The swirling of the two jets involved in the reaction can take placesuch that the two swirl flows are aligned in the same direction or inopposite directions. Swirling in opposite directions, i.e., swirling inwhich the swirl flows of the two gas streams in the contact area of thetwo gas streams are pointed in opposite directions to one another, hasthe advantage that the gas streams are mixed very vigorously with oneanother. The chemical reaction is accelerated, i.e., rapid, earlyignition of the reaction mixture of gases takes place. Swirling of theoverall jet that forms after combination of the gas streams isconversely relatively low, since the swirling of the reaction jets inopposite directions partially cancels the two original swirl flows. Theresulting flame thus widens relatively little.

Preferably, the individual swirl flows are aligned such that they run inthe same direction. In this case, the swirl flows intensify in thecontact area of the two gas streams, so that a relatively high totalswirl number is reached. This results in dramatic widening of theoverall jet. The speed along the jet axis decreases in the combustionzone. Based on the reduced jet speed, the dwell time of the reactants inthe reaction space increases compared to the known reaction guides inwhich at most one of the participating gas streams is swirled.

Moreover, with a suitable swirl intensity, a backflow relatively faraway from the burner tip can be produced. This leads to a circulationflow by which the gases remain longer in the reaction space and are thusbetter reacted. In particular, for slow chemical reactions, completereaction of the gas streams is achieved in this way.

The flame topology can be adjusted especially well for swirling in thesame direction. The axial length and radial extension of the flame canbe chosen and can be matched both to the reaction space and also to thereaction conditions. Moreover, the mixing of the two gas streams in thevicinity of the burner tip is not as intense as in the swirling of thejets in opposite directions, so that the thermal load on the burner tipis reduced.

Swirling in the same direction, moreover, has the advantage that at thedesired total swirl number, the swirl of one of the two gas streams canbe chosen to be lower than is possible in swirling in oppositedirections or in the known swirling of only one stream.

In the swirling of a gas stream, the gas stream necessarily undergoes acertain pressure loss. This pressure loss must be kept as low aspossible especially when the pertinent gas stream is available onlyunder low pressure. Under these circumstances it is advantageous if thegas stream under lower pressure is swirled less; the gas stream underhigher pressure is conversely swirled more strongly. The swirling of thetwo streams in the same direction thus makes it possible to achieve thedesired total swirl number.

The gas feed pipe is preferably made such that its inside diameterand/or its outside diameter decreases in the area of the exit end. Bychanging the inside diameter, the flow velocity of the gas in the gasfeed pipe can be influenced. The outside diameter especially preferablyapproaches the inside diameter in the vicinity of the exit opening fromthe gas feed pipe so that a sharp edge forms directly at the exitopening. On the sharp edge, the gas streams emerging from the gas feedpipe and from the surrounding ring channel break away in a definedmanner, by which unwanted eddies and turbulence are prevented.

The outside wall of the ring channel is advantageously tilted in thearea of the exit end in the flow direction of the burner axis. In thisway, the gas flowing in the ring channel meets at a certain angle thegas emerging centrally from the gas feed pipe, by which the mixing ofthe two gas jets is promoted.

It has proven advantageous for the outside wall of the ring channel inthe flow direction to extend beyond the exit end of the gas feed pipe.Damage to the gas feed pipe is, as mentioned, caused, on the one hand,by convection of the hot gases, but, on the other hand, also by heatradiation of the hot reaction gases. By pulling the outside wall of thering channel forward beyond the exit opening of the gas feed pipe, theangular area visible from the exit opening of the gas feed pipe isreduced. In this way, the conical area from which radiant heat cantravel directly to the gas feed pipe is made smaller, and the thermalload on the gas feed pipe is reduced.

Preferably, the gas streams supplied via the gas feed pipe and the ringchannel are combined at a certain angle to improve mixing of thestreams. After the two streams meet, the outer stream is widened by thecentral stream. The outer stream supplied by the ring channel thus movesfirst toward the burner axis and then away from the burner axis. If thischange of direction takes place too quickly, eddies can occur that canlead to backflow of hot gases to the gas feed pipe. Preferably,therefore, an annular guide sleeve adjoins the ring channel in the flowdirection; its outside wall runs essentially parallel to the burneraxis. The outer stream is thus deflected more gently, specifically fromthe original direction to the burner axis into a direction parallel tothe burner axis and only then away from the burner axis.

Advantageously, the ring channel or annular guide sleeve adjoins themixing chamber with an inside diameter that increases in the flowdirection. The flames are kept together by the latter, and combustion ispromoted.

It is advantageous if the means for producing a swirl in the gas feedpipe and/or in the ring channel have flow channels that are tiltedtangentially against the flow direction. One such execution of the meansfor generating a swirl can be easily produced, for example the channelscan be bevelled. The swirling of the stream can be easily dictated viathe angle of the flow channels. The swirling can also be produced viaappropriately aligned baffle plates, guide vanes or blades in the ringchannel and/or the gas feed pipe. This execution is to be preferredespecially when the pressure loss that occurs due to swirling is to beminimized.

Preferably the means for producing a swirl in the gas feed pipe and/orin the ring channel can be adjusted so that swirl flows of differentintensity can be produced. The flow conditions can be adapted to thesupplied amounts of gas and the chemical reaction underway by a suitablechoice of the swirl number, i.e., the intensity of swirling, of theparticipating gas streams. The load area of the burner can be adjustedin this way and especially can be enlarged.

Depending on the execution of the means for producing a swirl in the gasfeed pipe, in addition to the desired swirl, more or less strongbackflow at the end of this swirl generation means is formed. Thisbackflow can lead to hot reaction gases being sucked towards the burnertip and damaging it. It has therefore proven advantageous to provide theswirl generation means in the gas feed pipe with a central hole. As aresult of this hole, the central flow filament passes through the swirlgeneration means unhindered into the gas feed pipe. Backflow that formson the end of the swirl generation means is overcompensated by thecentral gas flow that runs essentially in a straight line. Downstreamfrom the swirl generation means, in this way, a swirl flow forms thatdoes not have flow components pointed backward in the center in thevicinity of the burner head. Damage to the burner tip is thus preventedespecially effectively.

Preferably means for supply with an oxygen-containing gas, especiallypure oxygen, are connected to the gas feed pipe and means for supplywith a combustible gas are connected to the ring channel. Feed of anoxygen-containing gas by the ring channel and a combustible gas by thegas feed pipe is also advantageous, however. In this case, means forsupply with a combustible gas are connected to the gas feed pipe, andmeans for supply with an oxygen-containing gas, especially pure oxygen,are connected to the ring channel.

In a preferred embodiment, there is a blade that stabilizes the gas flowin the gas feed pipe and/or the ring channel. At high differentialspeeds between the two gas streams in the end area of the line, eitherthe gas feed pipe or the ring channel through which a slower gas streamflows, eddies can form that can cause damage to the burner tip.Preferably, therefore, in the line in which the lower flow velocityprevails, a blade must be mounted that stabilizes the flow. The blade ismade such that the flow velocity in the forming channel is increasedbetween the wall separating the gas feed pipe and the ring channel andthe blade.

The blade is advantageously set back against the exit end of the gasfeed pipe or of the ring channel. This has the advantage that the bladeis located completely within one of the two gas streams. The gas streamcools the blade especially on its downstream end and prevents the hotreaction mixture of the two gas streams from coming into contact withthe blade.

There are advantageously different flow velocities for the twoparticipating gas streams, since in this way mixing of the two gasstreams is promoted. It has proven advantageous if the flow velocitiesof the gases differ by at least 10%, preferably at least 20%.

The absolute flow velocities are preferably between 30 and 200 m/s,especially preferably between 70 and 150 m/s, depending on the flamespeed of the gas in the current state. It has been shown that at thesespeeds the flow conditions following the burner exit can be adjustedespecially easily via the swirl number.

The ratio of the sum of the amounts of tangential pulses to the sum ofthe axial pulses defines the total swirl number. This influences, amongothers, the jet widening and thus represents the deciding parameter viawhich flame guidance and the dwell time of the gases in the reactionspace can be controlled. Preferably, the total swirl number is set suchthat it is between 0.1 and 1.2, preferably between 0.2 and 0.7.

The burner according to the invention is especially suited for definedchemical reaction of gaseous parent materials into a reaction product.The preferred use of the burner is primarily not to generate heat, butrather to carry out a defined chemical reaction of two or more gaseousparent substances. The gases can be optimally mixed in exactly definableranges by the double swirling. Here, the widening of the flame thatforms after the exit of the gases from the burner and the dwell time ofthe gases in the reaction space can be adjusted within wide limits andcan be adapted to the chemical reaction. The flame can thus be optimallymatched to the reaction space. The temperature in the reaction space andthe velocity distributions of the participating gases can be computedand matched to the desired process behaviors. The kinetics of thechemical reaction can be influenced.

In this respect, the process according to the invention has proveneffective especially in the chemical reaction of an oxygen-containinggas with a hydrogen sulfide-containing gas, with halogenatedhydrocarbons or pyrolysis oils or with low-calorie substances.Especially in the gasification of hydrocarbons that are reacted athigher temperatures with oxygen or an oxygen-containing gas, theefficiency of gasification is clearly increased. Basically the inventionis advantageous in all chemical reactions that are to proceed as near aspossible to chemical equilibrium.

The invention and other details of the invention are explained in moredetail below using the embodiments shown in the drawings. Here:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a section through a burner head according to the inventionand

FIG. 2 shows a section through the swirl body used for producing a swirlin the gas flow in the gas feed pipe.

The burner shown in FIG. 1 has a burner head 1 with a central hole inwhich a gas feed pipe 2 is located. The gas feed pipe 2 is connected toan oxygen supply that is not shown. The gas feed pipe 2 is surrounded bya ring channel 3 to which a combustible gas supply that is not shown inthe figure either is connected. The burner head 1 is furthermoreprovided with a cooling channel 14 for guiding a coolant, preferablywater.

The gas feed pipe 2 that is used as the oxygen delivery line runsslightly conically to the end in the downstream end area, the insidediameter and the outside diameter of the pipe 2 decreasing. On the exitend 4, the wall of the pipe 2 runs out at an acute angle. The ringchannel 3 is likewise tilted in the downstream end area against theburner axis 5. The outside wall of the ring channel 3 relative to theinside wall of the ring channel 3 and thus relative to the oxygendelivery line 2 is brought forward by a segment 6 with a lengthcorresponding to the inside diameter of the gas feed pipe 2. In this waythe angular range 7 that characterizes the “visual field” of the gasfeed pipe 2 is made smaller, by which the radiant heat of the hotreaction gases acting on the gas feed pipe 2 is reduced.

The ring channel 3 adjoins a guide sleeve 8 with an outside wall thatruns parallel to the burner axis 5. Downstream from the guide sleeve 8,the outside wall tilts away from the burner axis 5 and forms a mixingchamber 9 with an inside diameter that increases in the flow direction.The combustible gas flowing in the ring channel 3 is widened in burneroperation by the central oxygen flow. The combustible gas is thereforedelivered first to the burner axis 5 by the shaping of the ring channel3 in order to flow away from the burner axis 5 after leaving the ringchannel 3 in the mixing chamber 9 as a gas mixture with oxygen. Theguide sleeve 8 ensures that the change of direction of the combustiblegas takes place gently. The gradual deflection of the combustible gasstream prevents eddies and turbulence in front of the exit opening 4that could result in backflow of hot gas.

To improve intermixing of the combustible gas and the oxygen, there areswirl bodies 10, 11 located both in the oxygen delivery line 2 and alsoin the ring channel 3. The swirl bodies 10, 11 are set back relative tothe exit opening 4 of the gas feed pipe 2. FIG. 2 shows an overhead viewof the swirl body 10 in the flow direction. The swirl body 11 has,distributed over its periphery, several slotted channels 12 that runobliquely to the burner axis 5, i.e., they have an axial and atangential directional component. The swirl body 10 has an analogousstructure in the ring channel 3. A swirl flow is impressed on thecombustible gas and oxygen by the slotted channels 12 and leads toimproved mixing of the two gases in the mixing space 9.

In the ring channel 3, there are blades 15 that stabilize the gas flow.The blade 15 is made such that the flow velocity is increased in thechannel that is forming between the wall that separates the gas feedpipe 2 and the ring channel 3 and the blade 15.

Using the example of a Claus reaction, the invention will be explainedin detail once again. Claus systems are used to produce elementarysulfur from hydrogen sulfide-containing crude gas. The crude gas isburned substoichiometrically in a so-called Claus furnace so that sulfurdioxide and elementary sulfur are formed. The crude gas delivered to theClaus reaction generally also contains NH₃ must be essentiallycompletely reacted in the Claus furnace to form N₂ and H₂ or H₂O.Otherwise, unreacted NH₃ reacts with SO₂ and SO₃ further to form heavysalts that then lead to shifting in the Claus system over time. In thisconnection, especially the catalysts in the Claus reactors and thesulfur condensers are endangered.

To reliably break down NH₃, a temperature of greater than 1200° C. isrequired, and it must be ensured that the NH₃ is also in fact exposed tothis temperature. For this reason, it is advantageous to burn the crudegas with oxygen or oxygen-enriched air. This increases specifically theflame temperature, and decomposition of the NH₃ is promoted. Inaddition, very good intermixing of the gases in the flame must beensured because otherwise the NH₃ could transverse the Claus furnace inpart without having come into contact with the oxygen as the reactionpartner or without passing through the area with a relatively hightemperature. In both cases, the desired reaction into N₂ and H₂/H₂Owould not take place.

The burner according to the invention now enables defined intermixing ofthe crude gas with oxygen, relatively dramatic widening of the flame, sothat in the entire Claus furnace, the necessary temperature conditionscan be set, and the formation of the flow conditions in the furnace thatlead to an optimum dwell time of the gases in the furnace. The almostcomplete reaction of NH₃ into N₂ and H₂/H₂O is thus ensured.

1. A burner comprising a burner head, a gas feed pipe located in theburner head, and a ring channel which surrounds the gas feed pipe forfeed of another gas, means for producing a swirl of a gas flowingthrough the gas feed pipe, and the ring channel, wherein the wall of thegas feed pipe (2) runs to an acute angle on its exit end (4) and themeans (10, 11) for producing a swirl in the gas feed pipe (2) or thering channel (3) is set back upstream from the exit end (4) by 0.1 to 10times the outside diameter of the means (10, 11) for producing a swirl.2. A burner according to claim 1, wherein the means for producing aswirl located in the gas feed pipe has a hole that runs parallel to theburner axis.
 3. A burner according to claim 1, wherein the insidediameter of the gas feed pipe (2) decreases in the area of the exit end.4. A burner according to claim 1, wherein the outside diameter of thegas feed pipe (2) decreases in the area of its exit end.
 5. A burneraccording to claim 1, wherein the outside wall of the ring channel (3)is tilted in the area of the exit end in the flow direction of theburner axis (5).
 6. A burner according to claim 1, wherein the outsidewall of the ring channel (3) extends in the flow direction beyond theexit end of the gas feed pipe (2).
 7. A burner according to claim 1,wherein an annular guide sleeve (8) adjoins the ring channel (3) in theflow direction, and its outside wall runs essentially parallel to theburner axis (5).
 8. A burner according to claim 7, wherein the annularguide sleeve (8) is adjoined by a mixing chamber (9) with an insidediameter that increases in the flow direction.
 9. A burner according toclaim 1, wherein the ring channel (3) or is adjoined by a mixing chamber(9) with an inside diameter that increases in the flow direction.
 10. Aburner according to claim 1, wherein the means (10, 11) for producing aswirl in the gas feed pipe (2) and/or in the ring channel (3) have flowchannels (12) that are tilted tangentially against the flow direction.11. A burner according to claim 1, wherein the means (10, 11) forproducing a swirl in the gas feed pipe (2) and/or in the ring channel(3) are adjustable in order to produce swirl flows of varied velocity.12. A burner according to claim 1, further comprising means forsupplying an oxygen-containing gas, is connected to the gas feed pipe(2), and means for supplying a combustible gas is connected to the ringchannel (3).
 13. A burner according to claim 12, wherein saidoxygen-containing gas is pure oxygen.
 14. A burner according to claim 1,further comprising means for supplying a combustible gas is connected tothe gas feed pipe (2), and means for supplying an oxygen-containing gasis connected to the ring channel (3).
 15. A burner according to claim14, wherein said oxygen-containing gas is pure oxygen.
 16. A burneraccording to claim 1, further comprising a blade for stabilizing gasflow in the gas feed pipe (2) and/or the ring channel (3).
 17. A burneraccording to claim 16, wherein the blade is set back against the exitend of the gas feed pipe (2) or of the ring channel (3).
 18. A burneraccording to claim 1, wherein the means (10,11) is set back upstreamfrom the exit end (4) by 0.5 to 5 times the outside diameter of themeans (10,11).
 19. A burner according to claim 1, wherein the means(10,11) is set back upstream from the exit end (4) by 0.5 to 2 times theoutside diameter of the means (10,11).
 20. A process for producing areaction product by chemical reaction of gases that are supplied to areaction space by means of a burner according to claim 1, as twoseparate gas streams and are chemically reacted in the reaction space,wherein a swirl flow is impressed on the two separate gas streams beforeentering the reaction space.
 21. A process according to claim 20,wherein the swirl flows impressed on the two gas streams are in the samedirection.
 22. A process according to claim 20, wherein the flowvelocities of the two gas streams differ by at least 10%.
 23. A processaccording to claim 22, wherein the velocities of the 2 gas streamsdiffer by at least 20%.
 24. A process according to claim 20, wherein thetotal swirl number of the two swirl flows is between 0.1 and 1.2.
 25. Aprocess according to claim 20, wherein the flow velocities of the gasstreams are between 15 and 200 m/s.
 26. A process according to claim 25,wherein the flow velocities of the gas streams are between 70 and 150m/s.
 27. A process according to claim 20, wherein an oxygen-containinggas and a hydrogen sulfide-containing gas are chemically reacted.
 28. Aprocess according to claim 20, wherein halogenated hydrocarbons orpyrolysis oils are reacted with an oxygen-containing gas.
 29. A processaccording to claim 20, wherein hydrocarbons are reacted with anoxygen-containing gas for producing carbon black.